Field of the Invention
The present invention relates to a combustion apparatus and a water heater having the same.
Description of the Related Art
Specific examples of a combustion apparatus include the ones described in Japanese Patent Applications Laid-open Nos. 2013-231559 and 2005-69640.
In each of the combustion apparatuses described in Japanese Patent Applications Laid-open Nos. 2013-231559 and 2005-69640, heat shield plates are placed inside the side-wall portions of a burner case containing a burner. In each of the heat shield plates, at a position closer to the lower portion thereof, a substantially horizontal stepped portion is formed, and air passage holes are provided in the stepped portion. A part of air sent from a fan attached to a bottom portion of the burner case into the burner case upwardly passes through the air passage holes to flow upward along the inner side surfaces of the heat shield plate. This provides the effect of cooling the heat shield plate and the effect of the air flow inhibiting a flame from the burner and combustion gas from coming into contact with the heat shield plate. As a result, it is possible to inhibit the side-wall portions of the burner case from reaching extraordinarily high temperatures, while preventing heat damage to the heat shield plate.
However, as will be described next, the prior-art technique described above still has room for improvement.
Air sent from the fan into the burner case is intrinsically air for combustion to be used for the combustion drive of the burner. On the other hand, air upwardly passing through the air passage holes of the heat shield plate does not contribute to the combustion in the burner. As a result, when it is attempted to supply a large amount of air into the air passage holes of the heat shield plate, while controlling the amount of air used for the combustion drive of the burner to a proper value, it becomes necessary to increase the amount of air supplied into the burner case by increasing the size of the fan, the number of revolutions of the fan, or the like.
Water heaters include one which uses a heat exchanger of a type referred to as a single-case double-water-tube system in which two types of heat transfer tubes are contained in a side-by-side state in one case. In such a type of water heater, two burners are used to correspond to two types of heat transfer tubes and it is common practice to divide a region above these burners into two regions using a panel divider. It has conventionally been attempted to also cool the panel divider mentioned above using air in the same manner as for the heat shield plate described above. However, in such a case also, the same trouble as described above occurs.